PSA process and apparatus for the separation of a gaseous mixture

ABSTRACT

The device comprises an adsorber (1) and three outlet capacities (2-4), first (8, 9) and second (10, 11) structure to establish bidirectional communication between the adsorber and the elution capacity (2) and the repressurization capacity (3), respectively, and third structure (14A, 15; 16) to establish unidirectional communication from the adsorber to the production capacity (4).

CROSS REFERENCE TO RELATED APPLICATION

This application corresponds to French application 97 07117 of Jun. 9,1997, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to PSA apparatus for the separation of agaseous mixture comprising an adsorber and at least one output capacity.

BACKGROUND OF THE INVENTION

Mono-adsorber PSAs generally comprise a single capacity, simple or ofthe so-called segregation type, or two capacities, also simple or of theso-called segregation type. Examples are described particularly in U.S.Pat. No. 4,561,865 (Greene & Kellogg), U.S. Pat. No. 4,948,391 (VacuumOptics Corp.), U.S. Pat. No. 4,892,566 (Air Sep. Corp.), U.S. Pat. No.5,370,728 (Praxair) , U.S. Pat. No. 5,415,683 (Praxair) , U.S. Pat. No.5,565,018 (Praxair) , EP 0 663 229 (Sumitomo Seika), EP 0 743 087 (L'AirLiquide). The solutions with a single capacity are preferable as to costof equipment but do not permit optimization of the cycle nor volumes ofgas to be stored. The solutions with capacities of the segregation typepermit such optimizations but at the price of very high cost.

SUMMARY OF THE INVENTION

The present invention has for its object to provide a PSA apparatus andprocess for separation, permitting such optimizations at least cost.

To do this, according to one aspect of the invention, the apparatuscomprises:

an adsorber having a supply inlet for a gaseous mixture and a gasoutlet;

first, second and third capacities, the third capacity having an inletand a gas outlet;

first means to establish bidirectional communication between the outletof the adsorber and the first capacity;

second means to establish bidirectional communication between the outletof the adsorber and the second capacity; and

third means to establish unidirectional communication from the outlet ofthe adsorber toward the third capacity.

According to another aspect of the invention, the process for using suchan apparatus, comprises the successive steps of production, deeppressurization, elution and recompression, or:

in the production step, the gas product at the outlet of the adsorber isbrought by the second means to the second capacity and by the thirdmeans to the third capacity;

during the depressurization step, gas is brought from the outlet of theadsorber by the first means to the first capacity; and

gas from the first and second capacities is brought sequentially by thefirst and second means, respectively, to the outlet of the adsorberduring the steps of elution and recompression.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the present invention willbecome apparent from the following description of embodiments, given byway of illustration but in no way limiting, with respect to theaccompanying drawings, in which:

FIG. 1 is a schematic view of a mono-adsorber PSA apparatus with threecapacities according to the invention;

FIGS. 2 and 3 are examples of cycles according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, there is seen a PSA apparatus for the separation of a gaseousmixture, typically for the production of oxygen from atmospheric air,comprising an adsorber 1 and three outlet capacities 2, 3 and 4connectable respectively to the outlet of the adsorber 1, as will beseen further on. The inlet 6 of the adsorber 1 is connected to acompression/suction unit 7 with derivation valving as disclosed in U.S.Pat. No. 4,561,865 mentioned above or with a reversible rotary machine,as described in EP 0 743 087 mentioned above.

The first capacity 2 is connected to the outlet 5 by a line 8 comprisinga valve 9. The second capacity 3 is connected to the outlet 5 by a line10 provided with a valve 11.

The third capacity 4 comprises an outlet 12, or production outlet,connectable to a user circuit, and an inlet 13 connected to the outlet 5of the adsorber 1. In the embodiment shown in broken lines in FIG. 1,the inlet 13 is connected to the outlet 5 by a first section 14Aprovided with a non-return valve 15 then by a second section 14B. Theapparatus moreover comprises sequentially programmable control means 20for the first (9) and second (11) communication means and of the unit 7.

The operation of this apparatus will now be described with reference toFIG. 2 showing the phases of the PSA cycle.

As will be seen in this FIG. 2, the cycle comprises

a) a production phase in which the system 7 sends to the adsorber 1 apressure flow of gaseous mixture to be separated, the production gasseparated being brought to the second and third capacities 3 and 4 (thevalve 11 being open and the valve 9 closed).

b) a step in which the preceding adsorber in the production phase a) issubjected to a first co-current depressurization, the separated gas withfalling purity being brought to the first reservoir 2 (the valve 9 beingopen and the valve 11 closed). The pressure in this phase being lessthan the pressure reached at the end of the production phase, thenon-return valve 15 remains closed and the depressurization gas does notreach the production capacity 4.

c) a countercurrent depressurization phase, to the low pressure of thecycle, assisted by the system 7 operating as a pump.

d) an elution phase at the low pressure of the cycle by gas of mediumpurity from the first capacity 2 (the valve 9 being reopened).

e) an initial co-current repressurization phase by gas of high purityfrom the second capacity 3 (the valve 11 being open and the valve 9being closed), the valve 15 preventing any return of the gas in thecapacity 4 to a region of lower pressure.

f) a second pressurization phase by the gaseous mixture to be separated,without removal of production gas.

Such an arrangement permits reducing the dimensions of the storagecapacities whilst permitting an elution/repressurization sequence by gasseparated at increasing purity.

As a modification, the line 14B could comprise, in addition to or inplace of the non-return valve 15, a third electrovalve 16 controlled bycontrol means 20 in order, during the production phase a), to send theproduction gas sequentially first of all to the capacity 3 alone, andultimately to the capacity 4 alone, the valve 16 being maintained closedbeyond step a).

As a modification again, as shown in phantom line 14C on FIG. 1, thedownstream section 14A incorporating the nonreturn valve 15 could beconnected to the outlet 5, not directly but via the second capacity 3and its connection line 10 (the portion of line 14B is in this caseomitted).

In FIG. 3, there has been shown the cycle transposed from that of FIG. 2with this latter modification.

In the production phase a), all the production gas is sent to the smallsecond capacity 2 and then, from there, to the third capacity 4. Inphase e), upon the opening of the valve 11, the gas contained in thesecond capacity 3 returns to the adsorber 1 for its initialcountercurrent repressurization, the one-way valve 15 preventing anyreturn in the upstream direction of the production gas in the thirdcapacity 4.

As a modification, the cycle shown in FIG. 3 comprises no intermediatestep f) of repressurization by the single gaseous mixture to beseparated, the phase a) of production, with the valve 11 open, leadingdirectly to the initial repressurization phase e).

Although the present invention has been described in connection withparticular embodiments, it is not thereby limited but on the contrary issusceptible to modifications and variations which will become apparentto a person skilled in the art.

What is claimed is:
 1. A process for the separation of a gaseous mixturein a PSA device comprising an adsorber having an inlet for the gaseousmixture and a gas outlet for separated gas, and first, second and thirdcapacities selectively connectable to said gas outlet, the processcomprising a cycle including successive steps of production,depressurization, elution and repressurization, wherein:during theproduction step, the separated gas available at the gas outlet issupplied simultaneously to the second capacity and to the thirdcapacity; during the depressurization step, the separated gas istransferred from the gas outlet to the first capacity; during the stepof elution, gas from the first capacity is transferred to the gas outletof the adsorber; during the step of repressurization, gas from thesecond capacity is transferred to the gas outlet; and no gas from thethird capacity is returned to the adsorber.
 2. The process of claim 1,wherein the depressurization step comprises a final sub-step ofcountercurrent depressurization to a low pressure of the cycle.
 3. Theprocess of claim 2, wherein the final sub-step of countercurrentdepressurization follows a sub-step of depressurization toward the firstcapacity.
 4. The process of claim 1, wherein the repressurization stepcomprises a sub-step of co-current repressurization by gaseous mixtureonly.
 5. The process of claim 1, wherein the gaseous mixture is air. 6.The process of claim 1, wherein the gaseous mixture is air and oxygen isproduced therefrom.